The present invention relates to a gas channel forming plate that is arranged between a membrane electrode assembly and a plate-shaped flat separator and constitutes a separator of a single cell in a fuel cell, and to a fuel cell stack formed by stacking single cells.
For example, a solid polymer fuel cell includes a fuel cell stack, which is formed by stacking single cells. Each single cell includes a membrane electrode assembly and a pair of separators. The membrane electrode assembly is placed between the separators.
As such a separator, there is a separator including a plate-shaped flat separator and a gas channel forming plate that is arranged between a membrane electrode assembly and the flat separator (for example, refer to Japanese Laid-Open Patent Publication No. 2015-15218).
Grooves that extend parallel with each other are formed on a surface of the gas channel forming plate that faces the membrane electrode assembly. The grooves constitute gas channels, through which fuel gas or oxidant gas flows. The gas channel forming plate includes protrusions that are each formed between the corresponding adjacent pair of gas channels. In addition, grooves are formed on the back surfaces of the protrusions. The grooves constitute water channels for discharging water produced during power generation. The projections include communication passages through which the gas channels communicate with water channels and water in the gas channels is introduced to the water channels using capillary action.
In the fuel cell stack, water produced during power generation in the membrane electrode assembly flows out to the gas channels of the gas channel forming plate and is introduced to the water channels through the communication passages. The water is then discharged to the exterior of the water channels by the flow pressure of fuel gas or oxidant gas (hereinafter, referred to as gas) that flows through the water channels.
In the fuel cell stack, dry gas is introduced into the gas channels. Thus, a portion of the membrane electrode assembly that is close to the entrances of the gas channels is easily dried. Especially, at a low load time at which a small amount of power is generated, the amount of water produced during power generation in the membrane electrode assembly decreases. Thus, the membrane electrode assembly is more easily dried. As a result, movement of protons via water is hampered in the membrane electrode assembly, and it becomes a cause of decrease in the power generation performance.